1. Field of the Invention
The present invention relates to a vacuum fluorescent display, and more particularly, to a vacuum fluorescent display having complex-type filament supports, which include both a tension head and a tensionless head.
2. Description of the Related Art
A vacuum fluorescent display (VFD) is a type of electron tube that is able to recognize input/output states and operational conditions of various machines and apparatuses. VFDs are being used more and more frequently as a result of developments in various industrial machines.
The conventional VFD includes a vacuum container having an inner space that is maintained in a Vacuum state and provides a view area in one direction that is transparent, an anode provided within the vacuum container and receiving electrons to illuminate and display predetermined signals, filaments fixedly welded to a pair of filament supports to receive an external power and emit electrons, and a grid electrode for accelerating and diffusing (or for blocking) the electrons emitted from the filaments.
The vacuum container includes a lower substrate on which the anode is provided, an upper substrate (not shown) provided opposing the lower substrate at a predetermined distance form the same and formed to allow for easy passage of light therethrough, and a side glass formed between the lower substrate and the upper substrate at outside edges of the same to thereby seal the space between the lower substrate and the upper substrate. This space in the vacuum container is maintained in a high vacuum state to allow for easy emission and movement of electrons.
The filament supports fix both ends of the filaments such that the filaments are suspended at a predetermined distance from the anode. The filaments are supported by the filament supports such that a predetermined tension is provided in the filaments, even with the expansion of the filaments when they become heated.
Each of the filament supports includes a fixing plate welded to a mount of a lead frame, which is connected to the first substrate; tension heads, each corresponding to one of the filaments to fixedly secure the same; and tension arms interconnecting the tension heads and the fixing plate. The tension arms have a length L1 of approximately 2.5 mm in order to provide tension to the tension heads. A length of the tension arms in a state where the filaments are attached to the tension heads is L2. In the following, it will be assumed that the length L2 of the tension arms when the filaments are connected to the tension heads is the same as the length of the tension arms when the same are in a relaxed state.
The VFD including the conventional filament supports as described above has the following drawbacks.
If the frit glass for sealing the side glass and the lower substrate contacts the tension arms, the tension arms lose their tension such that they are unable to support the filaments. Further, if the frit glass is deposited on part of the fixing plates, when the frit glass is heated to seal the lower substrate and the side glass, cracks may develop in the frit glass as a result of the difference in thermal expansion coefficients between the frit glass and the filament supports. As a result, foreign substances (frit particles) are created so that the inside of the VFD becomes contaminated. Also, this causes the fixing plates to become loose or disconnected from the mounts to thereby cause shaking of the filaments.
To overcome these problems, a gap of 0.85 mm or more is maintained between the fixing plates and the side glass such that contact between the frit glass and the filament supports is prevented.
Therefore, in the VFD having the conventional filament supports, a significant amount of space is unable to be used by the anode electrodes as viewing space. That is, the 0.85 mm for the gap between short sides of the fixing plates and the side glass, and the length L2 of 2.5 mm for the tension arms when the filaments are attached to the tension heads combine for a total of approximately 3.3 mm that can not be used by the anode electrodes as viewing space. This increases the overall size of the VFD.